The present invention relates to a method for handing over a connection between a first and a second mobile communication network in a wireless terminal, in which method at least one data transmission connection is established for transmitting information between the wireless terminal and one said mobile communication network, wherein in the first mobile communication network, the connection type is either connection-oriented or connectionless, and in the second mobile communication network, at least two traffic classes with different transfer properties are defined, and one of them is selected for the data transmission connection of the second mobile communication network. The invention also relates to a communication system comprising at least a first and a second mobile communication network, a wireless terminal, means for activating at least one data transmission connection for transmitting information between the wireless terminal and one said mobile communication network, and means for connection handover between the first and the second mobile communication network in the wireless terminal, the first mobile communication network comprising means for establishing a connection that is connection-oriented and/or connectionless, and at least two traffic classes being defined for the data transmission connections in the second mobile communication network. The invention also relates to a wireless terminal comprising means for coupling to a communication system which contains means for establishing a data transmission connection to at least a first and a second mobile communication system, which first mobile communication system comprises means for establishing a connection that is either connection-oriented and/or connectionless, and in the second mobile communication network, at least two traffic classes are defined for the data transmission connections.
In this context, the connection handover refers to a situation when a connection is handed over from a wireless terminal which has a connection to a mobile communication network, to another mobile communication network. The wireless terminal refers, in this context, to such a data processor which also has means for establishing a data transmission connection to the mobile communication network. One example of a wireless communication device that can be mentioned is the Nokia 9000 Communicator, which comprises for instance data processing functions and mobile station functions.
In digital mobile phone systems, such as the GSM system, it is possible to transmit messages via a connection-oriented connection, such as a circuit-switched connection. A high-speed circuit-switched connection (HSCSD, High Speed Circuit Switched Data) can be mentioned as an example of such a connection-oriented connection. Furthermore, it is possible to transmit messages without setting up a circuit-switched connection. Such connectionless message transmission methods include for instance short message service SMS, unstructured supplementary service data transmission USSD, or packet based connectionless data transmission service GPRS (General Packet Radio Service). Consequently, in addition to calls and data transfer, the GSM system provides, in the form of the short message service, a service resembling a paging system. The short message service known from the GSM system is, however, much more advanced when compared with the conventional paging system. With a mobile station, it is possible not only to receive text messages but also to send them to another mobile station. Furthermore, one advantage of the short message service in the GSM system is that the transmission and reception of a short message can take place while a circuit-switched connection is open, for example during a call. Thus, the transmission of the short message does not keep the mobile station busy in the possible case of an incoming call.
In packet-switched data transmission, information is transmitted typically in bursts, wherein the interval between the transmission of bursts is influenced for instance by the quantity of information to be transmitted, and the amount of data transmission capacity allocated for the data transmission connection in question. The advantage of such a packet-switched data transmission connection when compared with a circuit-switched data transmission connection is that the data transmission channel allotted for the connection does not have to be allocated solely for one data transmission connection, but several different data transmission connections can use the same data transmission channel. Also in wireless mobile station systems, the circuit-switched data transmission connection is typically implemented in such a way that on the same radio channel, information of different connections is transmitted in different time slots (logical channels). When compared with the packet-switched connection, however, the difference is that even though there was no information in a data transmission connection to be transmitted in the time slot allocated for that data transmission connection, it cannot be utilized in any other data transmission connection either. A high-speed circuit-switched connection (HSCSD, High Speed Circuit Switched Data), which is under development for the GSM system, provides two connection types: a transparent connection and a non-transparent connection. In the transparent connection, the mobile communication network allocates resources for the connection in such a way that the connection has a substantially fixed data transmission rate and a fixed propagation delay. In the non-transparent connection, the mobile communication network can change the channel coding and data transmission rate when required by the circumstances, wherein it is possible for instance to ensure a better error correcting capability than in the transparent connection. The circuit-switched connection allocates at least one logical channel for the whole duration of the connection, which can unnecessarily consume the resources of the communication system.
As examples of the packet-switched data transmission services, the GPRS packet transmission service (General Packet Radio Service) of the GSM system and the packet transmission service of the UMTS system can be mentioned. These different systems and their different versions are not, however, fully compatible with each other. For example, the standard of the stage 1 of the GPRS packet transmission service deviates from the standard of the stage 2 and from the UMTS standard, e.g. with respect to the quality of service (QoS) alternatives that can be defined for the data transmission connection. Thus, when using a wireless terminal, the problem may arise, that a data transmission connection can only be established to a mobile communication network of a particular type, wherein the user should have a wireless terminal suitable for each mobile communication network available. To eliminate this problem, such wireless communication devices are being developed with which it is possible to establish a packet-format data transmission connection to two or more different mobile communication networks when moving from the range of one mobile communication network work to the range of another mobile communication network. In such a situation, the quality of service cannot necessarily be maintained on the same level in the mobile communication network to which a handover is attempted. For example, it should be possible to provide an audio telephone connection with high-speed packet transmission, so that speech would not become obscure and discontinuous at the receiving end. However, in the UMTS system, the aim is to achieve compatibility for instance with systems according to the stage 1 of the GPRS packet transmission service. This requires, for instance, solutions for the aforementioned problem: how to maintain the quality of service of the connection when handing over a data transmission connection from one packet network to another packet network.
It has been suggested that four different traffic classes be defined in the packet transmission service of the UMTS system, and as for the features of these traffic classes, the aim has been to take into account the different criteria for the different connection types. One criterion defined for the first and the second class is the real-time quality of the data transmission, wherein significant delays must not occur in the transmission. However, the accuracy of the data transmission is not such an important criterion. Correspondingly, for the third and fourth class packets, non-real-time data transmission is sufficient, but relatively accurate packet transmission is required. An example of real-time first-class data transmission is the transmission of speech signals in a situation where two or more people discuss with each other via wireless communication devices. An example of a situation where real-time second-class data transmission could be possible, is the transmission of a video signal for immediate viewing. Third-class, non-real-time packet communication can be utilized for example for the use of data base services, such as browsing Internet home pages, in which data transmission with moderate speed and accuracy is a more important factor than real-time data transmission. In the fourth class of this example system, it is possible to categorize for instance the transfer of e-mail messages and files. It is obviously not necessary to have four said traffic classes, but the invention can be applied in packet transmission systems containing three, two, or more than four traffic classes.
FIG. 1 is a block diagram showing the blocks essential for the function of the GPRS system. A serving GPRS support node SGSN controls the function of the packet transmission service on the cellular network side. The packet switching controller SGSN attends to the logon and logout of the wireless communication device MS, updating the location of the wireless communication device MS, and directing the data packets to the correct addresses. The wireless communication device MS is coupled to the base station subsystem BSS via a radio interface Um (FIG. 1) The base station subsystem is connected to the packet switching controller SGSN via a BSS-SGSN interface Gp. In the base station subsystem BSS, a base transceiver station BTS and a base station controller BSC are connected to each other with a BTS-BSC interface Abis. The packet switching controllers SGSN can communicate with other packet switching controllers SGSN via a gateway GPRS support node GGSN.
As presented in FIG. 2, the function of the wireless communication device MS and the packet switching controller SGSN can be divided into several layers, each having a different function. The information to be transmitted, such as control signalling and data sent by the user, is transmitted between the wireless communication device MS and the packet switching controller SGSN advantageously in a data frame format. The data frame of each layer consists of a header field and a data field.
The information contained in the data field can be, for example, data entered by the user of the wireless communication device, or signalling information. The functions of the layers of the GPRS system are presented in the following.
Lowest in the data link layer there is a MAC layer (Media Access Control), which is responsible for using the radio channel in communication between the wireless communication device MS and the base station subsystem BSS, e.g. allocating channels in packet transmission and reception.
Data transmission between the base station subsystem BSS and the packet switching controller SGSN on the lowermost level takes place in the L2 layer (data link layer), which uses a link layer protocol, such as the LAPD protocol according to the standard Q.921, a frame relay protocol, or the like. The L2 layer can also contain quality and routing data according to the GPRS specifications. The L2 layer contains features of the physical layer and the data link layer of the OSI model.
Above the MAC layer, there is an RLC layer (Radio Link Control), for the purpose of dividing the data frames established by the LLC layer into packets of fixed size that can be transmitted on the radio channel (PDU, Protocol Data Unit), and transmitting, and when necessary, re-transmitting packets. The length of the packets in the GPRS system is the length of one GSM time slot (ca 0.577 ms).
The LLC layer (Logical Link Control) provides a reliable data transmission link between the wireless communication device MS and the packet switching controller SGSN. The LLC layer, for instance, supplements the message to be transmitted with error correction data, by means of which it is possible to try to correct incorrectly received messages and, if necessary, the message can be retransmitted. Furthermore, data encryption and decryption is performed in the LLC layer.
Protocol modifications, compression and segmentation of the information to be transmitted, and segmentation of the messages coming from an upper layer are performed in the SNDCP layer (Sub-Network Dependent Convergence Protocol). The SNDCP frame comprises advantageously an SNDCP header and SNDCP field. The SNDCP header is composed of protocol data (Network Service Access Point Identity, NSAPI) and SNDCP control data, such as compression, segmentation and encoding definitions. The SNDCP layer functions as a protocol interface between the protocols (IP/X.25) used in the upper layer and the protocol of the LLC layer (data link layer).
The information to be transmitted enters the SNDCP layer from an application advantageously in data packets according to a protocol (PDP, Packet Data Protocol), such as messages according to the X.25 protocol or packets of the Internet protocol (IP). The application can be, for example, the data application of a wireless communication device, a telecopier application, a computer program which communicates with the wireless communication device, etc.
The SNDCP frame is transmitted to the LLC layer, in which the frame is supplemented with an LLC header. The LLC header comprises for instance an LLC control element, which specifies the number of the frame and the type of the command (info, acknowledgement, request for re-transmission, etc). When logging into the GPRS packet network, the wireless communication device transmits a login request message to the packet switching controller SGSN. On the basis of wireless communication device identification (IMSI, International Mobile Station Identity), the packet switching controller SGSN can retrieve information from a home location register HLR corresponding to the wireless communication device in question, wherein the packet switching controller SGSN can use this information to select a temporary logical link identity (TLLI) for the data transmission connection. If the wireless communication device has previously had a TLLI identity at its disposal, the wireless communication device transmits this in the request message, wherein the packet switching controller SGSN can allow this identity to be used again by the wireless communication device, or allocate a new TLLI identity. The packet switching controller SGSN transmits the selected TLLI identity to the wireless communication device to be used in the data transmission connection between the wireless communication device and the packet switching controller SGSN. This TLLI identity is used in the data transmission to define the data transmission connection in which the message in question belongs to. The same TLLI identity can only be used in one data transmission connection at a time. After the connection is terminated, the TLLI identity used in the connection can be given to a new connection which is being established.
The cells of the packet network are divided into routing areas in such a way that each routing area comprises several cells. Thus, the purpose of the mobility management functions of the wireless communication device is to maintain data on the location and connection state of the wireless communication devices in the service area of the packet network. This data is maintained both in the wireless communication device and in the packet network, advantageously in the GPRS support node SGSN.
In radio links, data is typically transmitted in a channel which is a particular frequency domain. One system can contain several channels which are available simultaneously. Furthermore, in full duplex data transmission, there are separate transmission and reception channels, wherein e.g. the base station transmits to the terminal via a transmission channel (downlink), and the terminal transmits to the base station via a reception channel (uplink). The problem with radio links is that the radio channel is a limited resource which restricts, for instance, the bandwidth that can be allocated for the radio link, the channel width used in the data transmission, and/or the number of channels and the data transmission rate available. The radio channel is liable to interference, such as distortion of the received signal caused by multipath propagation, that is, the same signal reaches the recipient via different routes at different times. To reduce the effect of interferences, part of the data transmission capacity has to be used to transmit error correction data with the packets, and it may require several re-transmissions of packets to achieve the desired error probability rate, which reduces the capacity of the radio link.
In such radio links where several data transmission flows are transmitted via one channel, the packets of these different data transmission flows are transmitted in time slots. The transmission order can be influenced by priorisation of packets of different data transmission flows, wherein packets of higher priority flow are transmitted more frequently than packets of lower priority flow. Such packets include, for instance, packets of a real-time application which are also aimed to be constructed as short as possible. On the other hand, packets of lower priority applications are often considerably longer than packets of higher priority. In systems of prior art, such a long packet prevents the transmission of other packets as long as the packet is transmitted. This may cause significant delays in the transmission of packets of even higher priority and impair the quality of service.
The term xe2x80x9cInternetxe2x80x9d is generally used to describe a data resource from which data can be retrieved with a data processor, such as a personal computer (PC). The data processor communicates with the telecommunication network via a modem. This information resource is distributed globally, and comprises several storage locations which also communicate with the telecommunication network. The Internet is made to function by specifying certain communication standards and protocols, such as TCP (Transfer Control Protocol), UDP (User Datagram Protocol), IP (Internet Protocol), and RTP (Real time Transport Protocol), which are used to control data transmission between the numerous parts of the Internet data network. The TCP and the UDP relate to preventing and correcting data transmission errors of data transmitted in the Internet data network, the IP concerns the structure of the data and routing, and the RTP is designed for real-time data transmission in the Internet data network. The Internet protocol versions currently in use are IPv4 and IPv6.
Packet-format data transmission enhances the utilization rate of the data transmission channel in general, not only for the purpose of retrieving information from the Internet data network. For example, packet data transmission can be used in applications such as audio calls, video conferences and other data transmissions according to different standards. However, some of these applications are time critical. For example in a real-time audio call, the best effort quality of service provided by the Internet protocol can cause significant delays in the transmission and transfer of the audio signal, which affects the comprehension of the received audio signal in such a way that for example speech becomes almost or totally unintelligible. Furthermore, the delay (the time passed between the transmission and reception of the packet) can vary during the transmission of the audio signal, depending, for instance, on the loading of the communication network and the variations in transfer errors. The same applies also to the transmission of a real time video signal. There may be situations, when the users of the Internet data network do not want such long delays which occur in many cases of data retrieval from the Internet data network.
The Internet Engineering Task Force (IETF) is an organization concerned with developing the Internet architecture and operating in the Internet data network. At present, the IETF is developing a new protocol which offers an Internet terminal a possibility to request for the desired quality of service QoS from the defined quality of service levels QoS available. This protocol is known as a resource reservation protocol (RSVP), and it is presented in the standard proposal xe2x80x9cResource ReSerVation Protocol (RSVP)xe2x80x94Version 1 Functional Specificationxe2x80x9d, Braden, R., Zhang, L., Berson, S., Herzog, S., Jamin, S., RFC 2205, September 1997 (available at the address http://www.isi.edu/div7/rsvp/pub.html). The Internet teminal uses the RSVP protocol when requesting for a certain quality of service QoS from the Internet network on the basis of the data transmission flow which the Internet terminal wants to receive from a remote terminal. The RSVP protocol transfers the request through the network by means of routers which the network uses to transfer the data transmission flow to the receiving Internet terminal. In each router, the RSVP protocol tries to allocate a resource for the data transmission flow in question. The RSVP protocol also tries to allocate a resource for the data transmission flow in the receiving and transmitting Internet terminal.
In order to conduct resource allocation in a node which can be either a router or an Internet terminal, the RSVP protocol communicates with two local decision modules, an admission control module and a policy control. The addmission control module deduces, whether the resources of the node are sufficient for providing the requested quality of service. The policy control module deduces whether the user has an access right to make the allocation. If either of the checkings is unsuccessful, the RSVP protocol returns an error message to the application that produced the request. If both the tests are successful, the RSVP protocol sets parameters for the classification and scheduling of the packet in the transmitting Internet terminal in order to attain the desired quality of service. The classification of the packet determines a quality of service class for all packets, and the scheduling controls the transmission of packets in order to achieve the promised quality of service in all data transmission flows.
The RSVP protocol functions on top of the Internet protocol both in the IPv4 and IPv6. The RSVP protocol is especially designed to utilize the strong features of the routing algorithms in the present Internet data network. The RSVP protocol does not perform the routing as such but it uses the lower level routing protocols to deduce where the allocation requests should be transferred. Because the routing changes the routes in order to adapt to changes in topology of the Internet network, the RSVP protocol adjusts its resource allocation to the new routes when necessary.
The standard proposal suggests two quality of service levels to be implemented in the RSVP protocol in addition to the existing best effort service: guaranteed service and controlled load service. The guaranteed service provides the connection with both a fixed transmission delay and a fixed bandwidth, and it is intended for transmitting e.g. a real-time audio call via an Internet connection. The purpose of the controlled load service is to provide the data transmission connection also in the loaded data transmission system with a quality of service substantially equal to that possible in an unloaded data transmission system. The controlled load service level is especially suitable for applications in which a considerable delay in the information transmission is allowed but, on the other hand, the aim should be to minimize the delay.
The purpose of the present invention is to find a solution e.g to the problem, in a connection handover situation, of how to implement the handover of data transmission connections active in a wireless communication device from one mobile communication network to another mobile communication network in such a way that the quality of service set for the data transmission connection at a time can be maintained as well as possible also in that mobile communication network to which the connection is handed over. The invention is based on the idea that when changing the mobile communication network, the active connections available in the wireless terminal at that moment and their traffic classes are examined, the traffic class corresponding to each connection is defined in the mobile communication network to which the connection is handed over, and a defined traffic class is set for each connection in said mobile communication network. The method according to the present invention is characterized in that in the method:
it is examined what active data transmission connections the wireless terminal has to the mobile communication network handing over the connection,
when handing over a connection from the first mobile communication network to the second mobile communication network, the connection type of each active data transmission connection is examined, the traffic class corresponding to each active data transmission connection type is defined in the second mobile communication network, and a connection according to the defined traffic class is established for each data transmission connection in the second mobile communication network,
when handing over a connection from the second mobile communication network to the first mobile communication network, the traffic class of each active data transmission connection is examined, the connection type corresponding to each active data transmission traffic class is defined in the first mobile communication network, and a connection according to the defined connection type is defined for each data transmission connection in the first mobile communication network.
The communication system according to the invention is characterized in that the communication system also comprises:
means for examining the active connections between the wireless terminal and the mobile communication network handing over the connection,
means for handing over the connection comprising:
means for examining the connection type of the active data transmission connections in the first mobile communication network, means for defining a traffic class corresponding to each active connection type of the data transmission in the second mobile communication network, and means for establishing a connection according to the traffic class defined for each data transmission connection in the second mobile communication network, and
means for examining the traffic class of the active data transmission connections in the second mobile communication network, means for defining a connection type corresponding to each active traffic class of the data transmission connection in the first mobile communication network, and means for establishing a connection according to the defined connection type for each data transmission connection in the first mobile communication network.
Furthermore, the wireless terminal according to the invention is characterized in that the wireless communication device also comprises:
means for examining the active connections between the wireless terminal and the mobile communication network handing over the connection,
means for handing over the connection comprising:
means for examining the connection type of the active data transmission connections in the first mobile communication network, means for defining a traffic class corresponding to each active connection type of the data transmission in the second mobile communication network, and means for establishing a connection according to the traffic class defined for each data transmission connection in the second mobile communication network, and
means for examining the traffic class of the active data transmission connections in the second mobile communication network, means for defining a connection type corresponding to each active traffic class of the data transmission connection in the first mobile communication network, and means for establishing a connection according to the defined connection type for each data transmission connection in the first mobile communication network.
With the present invention, considerable advantages are achieved when compared with methods of prior art. The method according to the invention enables a connection handover between mobile communication networks without terminating data transmission connections, and in such a way that the quality of service of the active connections is not impaired substantially. The invention enables, for instance, compatibility between the UMTS cellular network and the stage 1 of the GPRS system of the GSM cellular network in a packet-format data transmission. In the communication system according to the invention, it is possible to attain an effective use of the data transmission resources, for instance because in a connection handover situation, in the mobile communication network receiving the connection, resources are allocated for data transmission connections according to the quality of service allocated for the data transmission connection in the mobile communication network from which the connection is handed over.